Motor control system



April 8, 1947-- D. J. S'IKORRA 2,418,560

MOTOR CONTROL SYSTEM Filed March 16, 1944 Patented Apr. 8, 1947 UNITEDSTATES PATENT OFFICE Application March 16, 1944, Serial No. 526,753

8 Claims.

This invention relates in general to improvements in motor controlsystems, and more p rticularly to means for automatically varying theresistance of a motor circuit during starting of the motor.

The Starting current of electric motors, particularly direct currentmotors, is frequently limited by inserting resistors in circuit with themotor armature winding and automatically removing the resistors, oneafter the other, from the circuit While the motor accelerates to itsrunning speed. operation may be performed by switches of the contactortype which operate in response to the magnitude of the motor back E. M.F. or which are controlled by a relay responsive to the motor current.Such systems, however, require complicated interlocks or delicatelyadjusted switch operating means. The starting operation may also becontrolled by timing means which, however, no account of the rate ofacceleration. of the motor and may therefore cause the motor starting:current to be either too high or too low. The starting systems of theart also generally fail to operate uniformly for the reason that theiroperation is affected by the temperature of the operating coils utilizedtherein.

The above disadvantages may be avoided by controlling the switches forshort-circuiting the startin resistors by means of a rotary acceleratingrelay operable into a plurality of stable positions in response tovariations in two oppositely varying conditions of the system such asthe motor back E. M, and the voltage drop in the starting resistors. Theswitches for shortcircuiting the resistors may then be of a uniformdesign and the closing coils thereof may be selectively energized atfull line voltage, thereby insuring positive operation thereof.

It is therefore an object of the present invention to provide a motorstarting system which is differentially responsive to two inverselyvarying conditions of the system.

Another object of the present invention is to provide a mot r startingsystem operable in response to the motor back E. M. F, and to thevoltage drop in the starting resistors.

Another object of the present invention is to provide a motor startingsystem utilizing rotary means operable into a plurality of stablepositions in response to variations of at least one operating conditionof the system.

Objects and advantages other than those above set forth will be apparentfrom a consideration of the following description when read inconnection with the accompanying drawing, in which:

Fig. l is a diagram of an embodiment of the present invention consistingof a starting system for a direct current motor utilizing a rotary relayhaving the windings thereof connected in parallel with the motorarmature and with the starting resistors respectively.

Fig. 2 is an end View of the stator of the rotary relay utilized in Fig.1 showing the end connections of one of the stator windings;

Fig. 3 is an end View of the stator showing the end connections of theother stator winding, and

Fig. l, which is drawn on a larger scale than Figs. 2 and 3, is an endView of the rotor of the relay illustrated in Fig. 1 showing the contactsegments of the controller actuated thereby.

Referring more particularly to the drawing by characters of reference, adirect current motor comprising an armature winding 6 and a shunt fieldwinding l is to be supplied with current from a supply circuit 8, tenergized from a suitable direct current generator (not shown). Aplurality of resistors ill to 13 are serially connected with armaturewinding 6 for limiting the motor current upon connection of the motorwith circuit 8, 9 through the main contacts lea, Ilia of a pair of lineswitches l5, IS. The line switches are provided with operating coilsI52), I61) and switch I5 is also provided with auxiliary contacts llicto 51.

Resistors ill to [3 are controlled by means of a plurality of switchesl! to 2i! of the contactor type having pairs of contacts Ila to 20aseverally arranged in short-circuiting relation with the different.resistors. The closing coils llb to 201) of the short-circuitingswitches may be energized from circuit 8, 9 through contacts [5a, [6aand through a rotary controller generally designated by 22. Thecontroller comprises a plurality of contact segments 22a to 22d ofdifferent angular extent conductively connected with each other andseverally associated with contact fingers connected with coils ill) to2%. Segment 22a is further provided with a contact finger connected withone of contacts i5d. Controller 22 is also provided with a segment 22cfor bridging contacts liif and a starting push button switch 23.

Controller 22 is mounted on an insulated extension of the shaft Zia of arotary relay 24 of the torque motor type. Relay 2:! comprises a stator2th provided with two field windings 24c,

The field windings are preferably distributed over the bore of thestator as diagrammatically illustrated in Figs. 2 and 3 and areoverlapping to obtain a uniform action of the windings on the associatedrotor 24c. The rotor may be a wound or unwound block of ferroma neticmaterial or a permanent magnet.

The active conductors of windings 24c, 24d are preferably distributed onthe bore of stator 242) according to a sinusoidal law. Morespecifically, the number of conductors of each winding occupying a unitlength of the periphery of the bore is proportional to the sine of theangle defined by radii passing through the unit length considered andthrough a reference point of the bore. Although the conductors may bestrung within the bore of the stator it is generally preferred to insertthe conductors occupying each unit length in a separate slot. The statorslots and the periphery of the rotor are preferably skewed with respectto each other to render the action of the field windings on the rotormore uniform.

The arrangement of winding 240 in the stator slots is indicated in Fig.2 which shows the end connection of winding 240 only. There are noconductors in the top and bottom slots and the number of conductorsincreases from slot to slot to reach a maximum at the level of the rotoraxis. The end connections are between conductors at the same level toform a winding having a vertical magnetic axis. Winding 24d is similarto winding 240 but is relatively angularly displaced with respectthereto by 90 or by any other suitable angle and may be disposed in thesame slots as windin 24c. Winding 24d may be connected across circuit 8,9 through the lower portion 26 of a resistor having an adjustable tap,starting push button 23 and a stop push button 28, and may be connectedinstead u in parallel with resistors H! to [3 through contacts He andle. Winding 240 may b connected in parallel with armature winding 6through contacts 150, the upper portion 2! of the adjustable resistorand contacts [58. Controller 22 is thereby rendered operable into aplurality of stable positions, including a starting position in whichonly segment 22a is engaged, in response to variations in at least oneoperating condition of the system. The energization of the closing coils[5b, [6b of switches l5, I6 is controlled by contacts 29a of a marginalrelay 29 having the coil thereof energized from circuit 8, 9 throughcontacts l5f, push button switch 28 and two resistors 3!, 32. Anadjustable portion of resistor 32 may be short-circuited by contacts 290when relay 29 is deenergized.

Fig. 1 shows the elements of the system in the position reached therebyafter shutdown of motor 6, I. To initiate operation of the motor, pushbutton switch 23 is closed to cause current to flow from conductor 8through switch 28, switch 23, resistor 26 and winding 24d to conductor9. The flow of current through winding 24d produces a magnetic fieldcausing rotor 24a to rotate by substantially 90 to come into alignmentwith the magnetic axis of the stator, which is then the same as thegeometric axis of winding 25d. It will be observed that if rotor 24c isan unmagnetized block of ferromagnetic 1 material the rotor mayindifferently rotate clockwise or counterclockwise under the action ofwinding 2401 to thereby reach one or the other of two positions at 189from each other. As shown in Fig. 4, however, segments 22a to 22c areformed symmetrically with respect to the axis of shaft 2 3a so that thesame connections are efiected thereby at two positions difiering fromeach other by 180.

The position then reached by rotor 24c and iii) controller 22 is thestarting position wherein only segment 22c is engaged by the associatedcontact fingers. A circuit is thereby completed from conductor 8 throughswitch 28, switch 23, segment 226, coil 29b, contacts 290, a portion ofresistor 32 and resistor 3| to conductor 9. Relay 29 accordinglyoperates to open contacts 290 and close contacts 29a. Opening ofcontacts 29c inserts the entire resistor 32 in series with coil 29b tocause relay 29 to have a higher drop out voltage than any of switches l5to 20. Closure of contacts 29a completes a circuit from conductor 8through switch 28, switch 23, segment 22c, coils b and IE1) and contacts29a to conductor 9 to cause closure of switches l5, it. The switchesclose contacts 15a, Ilia thereof to connect armature winding 6 withcircuit 8, 9 through resistors Ill to 13 and to connect field winding 1directly across the line.

Contacts |5f then bypass switch 23 and segment 226 so that the switchmay be released by the operator. Closure of contacts l5e completes acircuit from the juncture point of armature winding 6 with resistor [3through contacts l5e and winding 24d to conductor 9. Winding 24d isthereby connected in parallel with resistors ill to [3 without openingthe circuit of the winding, but resistor 25 is thereby connected inparallel with armature winding 6 through contacts 150., switch 28,contacts I51, segment 22c and contacts l5e. Contacts 156 and I alsocomplete a circuit from conductor -8 through contacts 16a, contacts I50,winding 24c, resistor 21, contacts I52 to the juncture point of armaturewinding 6 with resistor I3, whereby winding 240 is connected in parallelwith armature winding 6 through resistor 21.

Upon closure of contacts 15a, 16a substantially the entire voltage ofcircuit 8, 9 appears across resistors 10 to l3, and winding 24d isenergized at substantially the full voltage of circuit 8, 9 whilewinding 240 is substantially without current. Controller 22 is thusmaintained in the starting position previously reached thereby. The flowof current through armature winding 6 and field winding 1 causes themotor to accelerate, whereby the back E. M. F. of armature winding 5increases gradually from Zero and the voltage drop in resistors ill toI3 decreases gradually from substantially line voltage. The flow ofcurrent increases in winding 24c and decreases in winding 24d to thesame extent and the magnetic fluxes produced by the windings varylikewise.

Rotor 24a is subjected to the differential action of the inverselyvarying currents of wind ings 24c, 24d to pass through a range of stableoperating positions. The effect of the current variation in windings24c, 2411 is gradually to shift the magnetic axis of stator 24b from thegeometric axis of winding 24d toward the geometric axis of winding 240.The relation be tween such shift and the increase in the motor back E.M. F. may be adjusted by displacing the tap of resistor 26, 21.Regardless of such adjustment, each pair of values of the back E. M. F.of armature 6 and of the voltage drop in resistors ill to l3 results inthe flow of currents in a predetermined ratio in windings 24c, 24d andin a. predetermined shift of the magnetic axis of stator 24b to moverotor 24c into a corresponding predetermined position. The position ofrotor 22c is stable as the rotor remains stationary as long as the ratioof the currents of windings 24c, 24d remains constant and also remainsstatlonary in the event that the windings are deenergized. I

During movement of rotor 24c, segment Z-Ze first disengages theassociated contacts to stop the flow of current through resistor 28which then performs no further useful function. Further movement ofrotor 24c causes a circuit to be established from conductor 8 throughcontacts Ilia, contacts lie, contacts d, segment 22o, coil I12) andcontacts l5a to conductor 8. Switch ll accordingly closes contacts I'mthereof to shortcircuit resistor iii. The flow of current througharmature winding which had decreased from its initial value to a valuedepending on the setting of relay 24, is thereby caused to increaseagain suddenly to a value depending on the re sistance of resistor illto cause further acceleration of the motor. It will be observed thatshort* circuiting of resistor it does not affect materially theoperation of relay 24. The reason therefor is that the back E. M. ofarmature winding 6 is determined only by the field current and the speedof the motor. The motor back E. M. F. and the voltage drop in theresistors there" fore unaffected by changes in the resistor connectionsand in the armature current, and the currents of windings 24c, 2M varyonly in dependence upon the changes in speed or" the motor. Theoperation of relay s also'unafiected by temperature changes, which causethe currents through the relay field windings to vary in the same ratio.

Further acceleration of the motor causes relay 24 to drive controller 22through. the ra o or operating positions thereof to establish circuitssequentially through the different segments 22b, 22c, 22d to causesequential operation of switches l8, l9 Upon closure of switch armaturewinding is energized at the full voltage of circuit 8, 8 and thestarting operation is terminated. Relay then re ins the position shown.in which winding d is without current and winding Me is energized at thefull voltage of c rcuit 8, 3 through resistor 2.1.

When it is desired to stop the motor, switch 28 is opened to interruptthe flow of current through coils i511, Iiib andv 2%. Relay 29 returnsto the position shown and opens contacts 29a. Switches 15, it open todisconnect the motor from circuit 3 and also deenergize the entirecontrol system. Relay 2 is thereby left in the operating position shownfrom which it must be returned to the starting position to start themotor in the manner above set forth.

The tap of resistor 32 is so adjusted that if, while motor 6, l isrunning, the voltage of circuit 8, ll drops below the normal valuethereof by a predetermined amount, relay to returns to the positionshown to open contacts thereby deenergizing coils it'll), its to shutdown the entire system,

Although but one embodiment of the present invention has beenillustrated and described it will be apparent to those skilled inv theart that various changes modification may he made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. A motor control system comprising an electric motor having a winding,resistor means serially connected with said winding, switch means forcontrolling said resistor means, and a rotary relay for controlling saidswitch means compris- Gil operable by the joint action of said fieldwindings flow of currents inten through said field windings.

Z. A motor control system comprising an electric motor having a winding,a plurality of resistors serially connected with said winding, a.plurality of switches severally controlling said resistors, and rotaryrelay cor prising relatively angulariy isplacco. field windingsconnected in parallel with said resistors and in parallel with saidmotor winding respectively, a polar magnetic element rotatably disposedin the resultant magnetic of said field windings, whereby said elementis rendered operalne by the joint action of said field windings intodifierent stable positions in response to the flow of current ofintensities in different ratios through said field windings, and aplurality of contact means actuated by said rotary element for causingsequential operation of the different said switches in response tomovement of rotary element through said positions.

3. A motor control system comprising an electric motor having a winding,a plurality of resistors ,rially connected with said winding, aplurality of switches severally controlling said and a rotary relaycomprising relalarly di held windings severally energized -n e to twodifferent; operating conditions oi a polar magnetic element rotatabiydisposed in the resultant magnetic field of said field whereby saidelement is rendered operable lo the joint action of said field windingsinto di' ent stable position in response t the flow of cu'rent ofintensities in different ratios through said field windings, and aplurality of contact means actuated by said rotary element for causingsequential operation of the different said switches in response tomovement of said rotary element through said positions.

4. A motor control system comprising an electric motor having a winding,resistor means serially connected with said winding, switch means forcontrolling said resistor means, a relay for controlling said switchmeans comprising an element having a starting position and meansconnected with said system for actuating said element from said startingposition into a plurality of stable operating positions in response tovariations in at least one operating condition of said system, means forshutting down said motor leaving said element in one of said operatingpositions, and means for initiating operation of said motor comprisingmeans for returning said element into said starting position. i

5. A motor control system comprising a source of electric current, amotor having a winding, resistor means serially connected with saidwinding, switch means for controlling aid resistor means, a relay forcontrolling said switch means comprising relatively angularly displacedfirst and second field windings and a rotary member operable by thejoint action of said field windings into a plurality of positionsincluding a starting position, second switch means for connecting saidmotor winding and said resistor means with said source, and means forinitiating operation of said motor comprising means for connecting saidfirst field winding with said source to cause said member to move intosaid starting position, means responsive to movement of said member intosaid starting position for causing closure of said second switch means,and means responsive to closure of said second switch means forconnecting said first field winding in parallel with said resistor meansand for connecting said second field winding in parallel with said motorwinding.

6. A motor control system comprising a source of electric current, amotor having a winding, resistor means serially connected with saidwinding, switch means for controlling said resistor means, relay forcontrolling said switch means comprising relatively angularly displacedfirst and second field windings and a rotary member operable by thejoint action of said field windings into a plurality of positionsincluding a starting position, and mean for initiating operation or"said motor comprising means for connecting said first field winding withsaid source to cause said member to move into said starting position andmean responsive to movement of said member into said starting positionfor connecting said first field winding in parallel with said resistormeans and for connecting said second field winding in parallel with saidmotor winding.

'7. A motor control system comprising a source of electiic current, amotor having a winding, resistor means serially connected wit saidwinding, switch means for controlling said resistor means, a relay forcontrolling said switch means comprising first and second windings and amember operable by the joint action of said first and second windingsinto a plurality of positions including a starting position, and meansfor initiating operation of said motor comprising means for connectingsaid first relay winding with said source to cause said member to moveinto said starting position, and means responsive to movement of saidmember into said starting position for connecting said first relaywinding in parallel with said resistor means and for connecting saidsecond relay winding in parallel with said motor winding.

8. A motor control system comprising a source of electric current, amotor having a, winding, resistor means serially connected with saidwinding, first switch means for controlling said resistor means, anaccelerating relay for controlling said switch means comprising firstand second windings and a member operable by the joint action of saidfirst and second relay windings into a plurality of positions includinga starting position, second switch means for connecting said motorwinding and said resistor means with said source, and means forinitiating operation of said motor comprising means for connecting saidfirst relay winding with said source to cause said memher to move intosaid starting position, means comprising a marginal relay connected withsaid source by movement of said member into said starting position forcausing closure of said second switch means, and means responsive toclosure of said second switch means for connecting said marginal relaywith said source independently of the position of said member, forconnecting said first accelerating relay winding in parallel with saidresistor means and for connecting said second accelerating relay windingin parallel with said motor winding.

DANIEL J. SIKORRA.

REFERENCES CITED lhe following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 653,470 Cutler July 10, 1900850,165 Knapp et al Apr. 16, 1907 1,306,548 McLain et al. June 10, 19191,311,754 Carichoii July 29, 1919 554,230 Berg Feb. 11, 1896 834,010Larson Oct. 23, 1906 1,030,617 Sill June 25, 1912 1,380,941 Axtell 1.June '7, 1921

